Color source



u@ 22, 1967 L.. R. EVENSEN ETAL. 3,336,835

COLOR SOURCE 2 Sheets-Sheet l Filed May 5, 1965 @rd/x0@ Wife/"Ugg u 22B967 l.. R. EVENSEN ETAL 3,336,835

COLOR SOURCE 2 Sheets-Sheet 2 Filed May 5, 1965 United States Patent O3,336,335 COLOR SOURCE Lester R. Evensen, Morton Grove, David A.Lieberman, Glenview, and Anthony W. Vering, Jr., Chicago, lill.,assignors to The Welch Scientific Company, Skokie, lill., a corporationof Illinois Fiied May 5, 1965, Ser. No. 453,308 16 Claims. (Cl. 88-24)This invention relates to a color source in general, and morespecifically is directed to a new and improved color head which isadapted for use with existing enlarger system, for example, that typesystem commonly known as a condenser-type enlarger. The presentinvention is also suitable for use in color analysis, reproductiondetermination and the like. For convenience, however, it will bedescribed in conjunction with a photographic enlarger and printer systemas deficiencies in existing designs were the principal stimulant in itsdevelopment.

The prior art is replete with a variety of printing techniques,processes, materials and different approaches all aimed at obtaining asuccessful and expedient method of printing color photographs. Even themost successful of these `attempts involves a certain amount of cut andtry techniques or repeated adjustment and measurement in order to obtainthe necessary color balance. This is primarily due to deficiencies orinadequacies of the printing apparatus.

One of the more widely used methods of printing techniques involvesmulti-layer dye coupling type paper readily available on the openmarket. The individual layers are sensitive respectively to red, greenand `blue light to release the dye. Cyan, magenta and yellow layers formthe negative film to be printed, which layers are responsiverespectively to adjust the level of the red, green and blue lightreaching the paper. Such negatives are obtained through the exposure anddevelopment of such film known by the trademarks Kodacolon Ektacolor andthe like.

When a negative of the type described is exposed through the use of aconventional white light source, i.e., a conventional light bulb, thesensitive layers of the paper are not only responsive to the specificwave lengths of red, green and blue contained in the white light butwill also respond to wave lengths above, below and between the red, blueand green Wave lengths. Accordingly, unwanted portions of the whitelight sensitize the various layers resulting in a print which issomewhat removed in color proportions from the negative.

When light from a single source is used, a true balance between thethree colors is almost impossible to achieve because the exposure ofeach of the respective layers in the paper is dependent upon time andintensity of exposure to the appropriate sensitizing color. As expected,each of the dyes in the paper have different response rates while theinterval of exposure is obviously the same for all colors when a singleexposure source is used, Various attempts have been made to subtract, bythe use of filters, the unwanted light and wave lengths to bring thecolor balance to a reasonable approximation necessary to obtain a printof at least marginal quality. This procedure is sometimes identified asthe subtractive process of color balancing and is vulnerable to a numberof criticisms by those working in the field, since it generally requiresmore exposure time by slowing down the response time of the respectivedyes in order to Ibring the same to a closer common time interval ofexposure for each color. The large light losses caused by this as wellas the testing and checking prior to printing consume a great deal ofthe printers time as Well as tying up the enlarger for a considerableperiod. Even in those cases when a reasonably good color balance isultimately achieved, it is unstable being susceptible to drift becauseof the change in value of the lters due to heat, aging, exposure to highintensity light and the like. In summary, while the above technique isnot a complete failure, it is far from what could be consideredcommercially desirable.

Notwithstanding the criticism of the subtractive filtration arrangement,it is in use by photographers since it is the most expedient andconvenient of known and operable printing and enlarging systems to date.One specific cornmercial structure in use today utilizes a subtractivefilter system in combination with an integrating sphere `and two lightsources. The subtractive filters in this design are subjected to thecriticisms noted above while the integrating sphere provokes additionalcriticism since it does not provide the desired fineness of control andleaves something to `be desired when the efficiency of the light isanalyzed.

In the past when a truly balanced print has been desired, successiveexposure of each of the layers has been recommended. In this process,filtered red, green and blue light is transmitted consecutively throughthe film negative, permitting a higher color purity to be achieved. As ageneral rule, in this process the color purity has been controlled bythe use of lters disposed between the negative and the print paper, withthe obvious adverse effect on image definition. Other disadvantagesmainly in the time required, exist which makes the successive exposuretechniques impossible for competitive type color printing work.

In general, in all systems, subtractive filters have also beenundesirable since one filter will properly compensate to remove anunwanted band of color but at the same time will have an adverse effecton the level of color of an adjacent band. In checking the color balancein the subtractive process, it is necessary to insert filters in thepath of the light and check each of the respective colors at variouspositions on the easel to determine and adjust for lthe exposure timeand color balance. A probe, provided with filters, is used to check theintensity of each of the color components. Adjustments may be made byadding or suhtracting filters to effect a color balance. Since filtersare needed at the probe, the efiective light intensity is lowerednecessitating a more powerful amplifier, as well as a preamplifier inthe probe which adds to its bulk. In addition, a need exists tophysically touch the probe to shift from one filter to another. If theprobe is moved slightly, as lby an accidental bump, it becomes necessaryto repeat the color measurement with the former time and effort wasted.

The foregoing problems are but a few examples of the difficultiesexperienced in the past, which gave impetus to the development of thepresent invention. During this development, these objectives wereattained. The interaction of filters was eliminated in order that therespective color levels could-be chosen with a single light probe test.The system was accurate whereby the usual correction factors provided onthe box of the printing paper could be readily compensated for, thusmaking this information more useful. Various switching between and useof subtractive filters in the probe and enlargers was eliminated inorder to minimize the number of adjustments, and therefore minimize thepossibility of printers error.f The elimination of the filters in theprobe also permitted the use of a simpler probe and lower gain amplifierwith the obvious advantageous effect on sensitivity. Elimination of.subtractive filters in the enlarger increased the efiiciency of thelight. In addition, exciting light is refined to the peak response ofthe individual layers of the photographic paper to avoid simultaneouslystimulating adjacent layers. A small but further correction providesrened light whose peaks fall within the range of peak response of theindividual layers of the photographic paper and are still within a moresensitive wave length -range of known types of phototubes. The systemrequired a minimum number of special parts while making highly eflicientuse of the available light.

Y The present invention provides a new and improved color head whichsolves the above noted problems and achieves all the stated objectives.-It is capable of providing an additive light source permittingsimultaneous balanced exposure of the sensitive layers of photographicpaper since this light source, through a unique lens and multi film ltersystem, provides a coaxial white light composed-of color componentswhich are of a well defined band width and which for all practicalpurposes are nonoverlapping.

Simple adjustment and balance of each of the respective colors may beindividually affected without any effect on the intensity of the othercolors thus requiring minimum light level testing before printing maybegin. The effect of this on the printing time is obvious. The presentsystem is highly accurate and provides means whereby the `correctionfactors given with each supply of printing paper may be used to theirfullest potential. With the present system the simplest type of probeand a relatively sensitive low gain amplifier may be used to balance therespective color components to an appropriate level of intensity.

The present invention, through a unique and unobvious solution of theproblems enumerated, provides a system whereby the problems of the priorart may be avoided. A

number of advantages in addition to those enumerated ow from the novelsolution about to be described. A better comprehension of theseadvantages as well as the salient features of the invention may be hadby a consideration of the objects to be achieved and a detaileddescription of a preferred form of the invention which follows.

It is a principal object of this invention to provide a new and improvedcolor source for photographic printers and the like.

It is another object of this invention to provide a color head whichpermits simultaneous exposure of multisensitive layers of photographicpaper, exposure of each layer being easily and accurately controlled.

It is a further object of this invention to provide a new and improvedcolor head which provides a white light source composed of colorcomponents of blue, green and red with each of the colors beingindividually controlled without affecting the other and with each colorfalling within a wave length band which does not overlap the adjacentcolor or extend substantially above or below the visible region of wavelengths.

It is a still further object of this invention to provide a new andimproved color head which is adapted to replace the light head of anexisting enlarger.

It is a still further object of this invention to provide a new andimproved color head which provides a white light source composed of theadditive primary colors and which has suiiicient intensity to permittest equipment of relatively low gain to be used in testing the colorbalance prior to printing, and further which reduces the time ofprinting by permitting a simplified adjustment of each of the colorlevels.

It is a still further object of this invention to provide a new andimproved photographic enlarger head which is capable of use withexisting condenser type systems and further wherein a novel lter meansis provided which permits both hard and portrait type prints to beprinted on the same apparatus.

Further objects will become readily apparent when reference is made tothe accompanying drawings wherein:

FIG. 1 is a perspective view of the color head of the present inventionapplied to a conventional type condenser enlarger;

FIG. 2 is an elevational view of the color head shown in FIG. l with theshield removed;

FIG. 3 is a top plan view of the color head as shown in FIG. 2;

FIG. 4 is a side elevational view of one of the light sourcesubassemblies;

FIG. 5 is a schematic diagram of the system shown in FIG. l; and

FIG. 6 is a graph of light transmittance (in percent) plotted againstwave lengths for the visible region with the solid lines representingtheoretical calculations taking into account the limitations ofmeasuring phototube while compensating for the three layer peak responseand the dash lines representing one workable set of wave lengths takenfrom the system of FIGS. 1 5.

Referring now to FIG. l, an enlarger system is represented generally bythe reference character 10 including a color head ll having a condenseradaptor i2 at the lower extremity. A condenser system 13 and negativeholder 15 of conventional design are disposed above an adjustable lengthbellows 14 which terminates in a focusing system 16 positioned above aneasel schematically represented by the rectangle 1'7.

The color head 1l through use of the condenser adaptor l2 and uniqueoptical design may be used with any known type of system whichheretofore has used a single light source- The optical design andgeometry of the present invention is such that it terminates andpresents the appearance to the condenser assembly of being a singlewhite light point source evenly diffused into a perfect circle while inactuality being composed of three distinct colors of readilyidentifiable and well defined wave lengths.

Referring now to FIG. 2, the color head 11 is illustrated with the caseor shield removed, generally displaying three separate light sources2l), 2 1 and 22 arranged in vertical relationship above the condenseradaptor 12. Each of the light sources has a'n optical land geometricaxis which intersects a common vertically disposed central axis 30coincidental with the geometric axis of the cylindrical condenseradaptor 12.. Expressed another way, horizontal planes passing throughthe axis or center of each of the light sources 20, 21 and 22 arevertically spaced and parallel to each other and intersect a verticallydisposed central axis 30 at righ-t angles.

The condenser adaptor 12 is broken away in FIG. 2 to illustrate asemisphere subassembly 23 which is also broken away to illustrate themounting arrangement. The semisphere subassembly includes a mountingtube 24 held in a bracket 25 which is disposed below the light source2li. The mounting tube 24 houses an aspheric lens 26 at its upper endand a plano-concave or negative lens 27 at its lower end. A diffusingsemisphere 28 is suspended from the lower end of the mounting tube 24.

Suitable retaining means may be provided to hold the lens in theposition shown with the dimension between the two lenses 26 and 27 beingcarefully and accurately controlled. When the lower end of the colorhead 11 is viewed in elevation, the appearance of an ordinary singlelight source is presented making it suitable to replace a single lightsource.

As seen in the top plan view of FIG. 3, the sources 2l), 2l and 22 arearranged about a central axis 30, angularly spaced in azimuth by 45. Asseen in FIGS. 2 and 3, the central axis 30 is coincidental with thegeometric axis of the mounting tube 24 and condenser adaptor 12. Theimportance of the coaxial arrangement of each of the light sources 2t),2l and 22 will become apparent.

The angular spacing of the light sources 20-21, among other thingsserves to allow the separation between each of the individual lampscontained in the light source with- 1n good design geometry in order tofacilitate a good cooling or heat dissipation during operation of theenlarger. To enhance this effect, a blower (not shown), is

mounted in a convenient location remote from the er1` larger support orpedestal and supplies cooling air through a flexible tube (not shown) tocool the color head 11. Through the remote mounting, vibrations inherentin the operation of the fan, particularly when it becomes worn from use,will not be transmitted to the enlarger head to cause a vibration duringprinting.

Referring now to FIG. 4, the light source 21 is illustrated with partsin section to present a clearer understanding of the more detailedfeatures. A light source holder or mount 31 may be formed in anysuitable manner by machining, casting or the like. The holder 31 isprovided with an upstanding bracket portion 32 which threadably mounts aplurality of thumb screws 33 for movement along their respective axes inresponse to rotation. The thumb screws 33 at their inner end mount aspherical mirror 34 which may be adjusted towards and away from a lamp35 mounted in a lamp socket 36 on the light source holder 31. The lamp35 is of a type known as having a prefocused base so that when insertedin the socket 36, the lament 37 will be in the same location relative tothe base for all lamps within a specified close tolerance.

The light source holder 13 is provided with an annular chamber 38terminating adjacent the lamp 35 in an inwardly projecting flange 4f),counterbored as at 41 to receive a positive meniscus lens 42. Anenlarged bore 43 adjacent the lens 42 has an enlarged counterboredportion to form a mount for a double convex lens 44. The lens 42 is heldwithin the counterbored portion on the fiange 40 by a retaining ring 45while a larger diameter retaining ring 46 holds the double convex lens44 in its mounting in the counterbored portion of the enlarged bore 43.Each of the counterbored portions is very carefully machined in orderthat the lenses 42 and 44 may be accurately placed relative to eachother and the lamp 35. The positive meniscus lens 42 serves to initiatecollimation of the light from the lamp 35 and for convenience will beidentified as a first collimator. The double convex lens 44 serves tocollect and arrange light rays from the first collimator 42 intoparallel rays and will be identified as the second collimator.

As is well known in optics, when theoretically designing a light system,it can be assumed that the light sources are point sources and light isuniformly passed by each lens. However, in actual practice where thesources are lamps, the filaments have a finite dimension, and chromaticaberration is normally experienced. In systems where the light intensitylevels are of low order, for all practical purposes the size of thefilament can be ignored as well as aberration. However, in an enlargersystem such as the present where a high level of light is required, thefilament size will run on the order of about several millimeters square.Accordingly, the collimating system shown was developed to accommodatethis finite size of the filament and avoid aberration or non-uniformityin the intensity of the beam of light when viewed in cross section.

At the outer end of the bore 43 is provided a filter mounting means orholder 47 which is held in place by suitable mounting means such as thescrews 43 received in tappings in the holder 31. Two permanent filtersare shown at 5ft and 51 clamped within the filter mounting means 47 andserve to refine the collimated white light from the lamp 35 into aselected color having a wave length falling within selected limits forone of the additive primary color components.

An additional filter 52, which is sometimes referred to as a dichroicfilter, is held to machine surfaces 53 and 54 on the light holder 31 bymeans of screws and clamps 55 and 56 respectively. The dichroic filter52 is arranged at a perfect 45 angle relative to the collimated light sothat the incident and refiection angles are equal to 457 thereby todirect collimated and filtered light through the aperture 57 in theholder 31. The aperture 57 has its cen- 6 ter coaxial with the centralaxis 30, as do the apertures on the light sources 20 and 22.

The light source 2t? is physically identical to the light source 21, anddifiers optically only in the selection of filters to be substituted forequivalent filters 5f), 51 and 52. Similarly, light source 22 isphysically identical to light source 21 with the exception that a singlefilter is substituted for the two filters 5t) and 51, and a dichroichaving a different reflectance wave length is substituted for thedichroic 52.

The spherical mirror 54 may be adjusted at the factory to focus themaximum amount of light from the filament 37 of the lamp 35 back to thefilament so it is directed toward the first collimator 42. Through theuse of a prefocused base 36, the lamp 35 when no longer operative, maybe readily replaced by a similar lamp without affecting the opticalrelationship of the filament 37 relative to the collimating lens system.The collimating lens system, composed of the first collimator 42 anddouble convex lens 54 forming the second collimator, collimates thelight into parallel bundles, directing it to the lters which byselection reject all light above and below selected wave lengths. Abetter understanding of the optical characteristics and types of lensesand filters will be given when FIG. 5 is described.

The intensity of the lamp 35 may be adjusted by the variable resistanceshown schematically at 60. In a typical case this resistor comprises a-ohm 22S-watt resistance to provide a good range of intensityadjustment. Additional resistors may be placed in series and factoryadjusted to obtain a reduced operating voltage to the lamp 35 for longlife. A preheat circuit may be provided t0 keep the filaments warm andfurther extend their life. With the arrangement shown, the power to thelamp 35 may be varied to raise and lower the intensity level forpurposes noted above.

Ordinarily resistance control of light in enlargers has not been'successfully used in the past even though highly desirable, because itserved to change the color temperature of the lamp. For example, theblue colors change at a faster rate than the reds. Due to the novelsystem of filters, the refined light band is relatively narrow, and anyshift of intensity of one color has no effect on the other colors. Theadvantages of resistance control are self-evident permitting a widerange of intensity levels to be selected with unequaled ease.

In FIG. 5 the enlarger system 10 is illustrated in schematic form andlike reference numerals have been given to common elements including thefirst and second collimators 42 and 44, lamps 35 and mirror 34 of eachof the respective light sources 20, 21 and 22. In light source 20,vertical filters 62 and 63 are provided to filter the collimated whitelight into a band falling between about 610 millimicrons and into theinfrared region or about 740 millimicrons. The upper limit will bedefined by a subsequent lter. A 45 dichroic filter 64 is arranged inparallelism with the dichroic 52 and disposed in the path of thecollimated light so that the angles of incidence and refiection will beequal to 45.

Contrasted with the lower light source 21, the upper light source 22 isprovided with a single vertically disposed filter 65 which is sometimesreferred to as a 90 filter. The angularly arranged filter or dichroic 66is located relative to its collimated light source such that the anglesof incidence and reflection of the collimated light will be exactlyequal to 45 which is parallel to the dichroics 52 and 64. All of thedichroics 52, 64 and 66 are arranged so that the angle of reflection ofeach will be coincidental with the central axis 30 to provide a refinedcoaxial white light.

The or transmitting filters 50, 51, 62, 63 and 65 allow only light of aspecified or definite wave length to pass and are chosen and identifiedby their transmittance value. Conversely the dichroics or separatingfilters 52, 64 and 66 are chosen to refiect only the desired color oflight while transmitting or passing all that is not reflected. Whenfigured on the basis of 100%, or perfect transmittance, and contrastedto colored glass, dyes and other type filters, the multi film filtersselected absorb practically no light. Their transmittance at anyselected wave length in the spectrum is determined by their refiecanceat that wave length and accordingly when either of these factors isadjusted, the other increases or decreases in a compementary manner.

In the present system the filter 65 is designed to reflect all visiblelight above about 480 millimicrons. It transmits a preponderance (90%)of visible light wave lengths falling between about 380 and 425millimicrons. The associated dichroic or separating filter 66 passesalmost all visible light above about 610 millimicrons while wave lengthsbelow this value are reected along the axis 30. The lower range of thespectrum is reflected including ultraviolet rays which may be present,however, these are filtered out as will be seen. A preponderance ofrefiectance (over 90%) is experienced in the band from about 400 to 560millimicrons.

Filters 50 and 51 are chosen to transmit vlight having a wave lengthfalling generally between 520 and 600 millimicrons being what iscommonly known as the wave length band `for green light. The associateddichroic or 45 separating filter 52 is designed to pass all light aboveand below the noted wave length and to reflect a band width of about 500to 590 millimicrons at a 90% reflectance capability. Accordingly, thegreen color component is well defined and readily identified.

Multi film lters 62 and 63 in the lower light source 20 are chosen topass all light above about 600 millimicrons including some wave lengthsextending into the infrared range. The associated dichroic filter 64 hasa reflectance characteristic to reflect virtually all wave lengths above630 millimicrons at 90% reflectance while transmitting other wavelengths. Accordingly, the separating or dichroic filter 64 serves totrim the lower end of the band by some 30'millimicrons to furtherseparate it from the adjacent green component.

A 90 filter 67 is provided to suppress ultraviolet wave lengths or thosewave lengths below about 400 millimicrons passing all visible wavelengths above. A second filter 68 acts as a heat absorber to transmitwith about 50% or `greater efiiciency, those wave lengths fallingsubstantially within the visible region between an upper limit of 700and the lower ultraviolet cut off of 400 millimicrons effected by filter67. Accordingly, higher value wave lengths of infrared will besubstantially suppressed with a small controlled portion passed.Unwanted ultraviolet light which is normally considered to be below 400millimicrons is sharply cut off.

When the light sources 20, 21 and 22 which are red, green and bluerespectively, are energized, refined white light consisting of threeidentifiable and individually controllable well defined color componentswill be generated. At printing intensities, each of the colors isnon-overlapping with adjacent colors. Light source 22 will provide tothe aspheric lens 26 light falling within 400 to 480 millimicrons with apeak transmittance falling slightly below what in theory is identied aspure blue. In a similar manner, the light source 21 will provide thegreen component of light which will be blended with the light from theblue source 22. This light has a wave length of about 520 to 590millimicrons with a peak or maxi mum transmittance experienced at about550 millimicrons as seen in dotted lines in the graph of FIG. 6. Thelower light source 20 will provide the red component of light, since ithas a wave length of from about 600 millimicrons out into the infraredrange slightly in excess of 700 millimicrons.

All three light sources, due to the selection and arrangement of thefilters will provide a coaxial band of light of uniform intensity. Itcan be appreciated that each of the separating filters 52 and 64 has atrimming effect on the color component reflected from the sourcesdisposed above the same. The accurate collimation provided by the uniquecollimating lens selection and arrangement, directs the light to thefilters at the proper incident angle. This is very critical as it avoidsresonance conditions which arise when the light strikes the filter atnon-unform incident angles, a common occurence when the light is notcollimated. The light rays of the three color components are blendedtogether with the unwanted portion of ultraviolet filtered out throughthe filter 67. The infrared wave lengths are controlled by thesuppressor 68 to permit a small percentage to pass to enhance printing.

The aspheric lens 26 is of a special design to focus the blended colorcomponents to a focal point which is coincident with that of thenegative lens 27, the latter serving to evenly diffuse or spread thelight to ll the semisphere 28. If desired, the plane surface of theplanoconcave lens 27 may be etched, sand blasted, or the like to providea diffusing surface to fill the semisphere 28 with light. Obviously, aseparate diffuser may be provided as an alternative, however, ideallythe diffuser should be as close to the plane surface as possible. Thesemisphere 28 is a sphere truncated substantially above the geometriccenter and may also be provided with a diffusing type etch, sand blast,coating or the like on either the interior or exterior surface or both.It serves to diffuse the light evenly to the condenser system 13containing the usual condenser lenses 71 and 72 both of which are ofconventional design and serve the conventional function. When viewingthe semisphere 28 back through the edges of the condenser lens, aperfect circle of light is seen which indicates that the light isuniformly received by the condenser system from the source fortransmission to the focusing lens 16. Accordingly, more uniformity inintensity at the corners of the print will be experienced.

The negative holder 15 receives the negative and in addition hassufficient vertical clearance to accommodate an additional filter whichwill be described. A color compensating lens 74 mayalso be providedimmediately above the aspheric lens in those situations whereinenlargements of unusual size are to be made. This lens is indicated inthe diagram at 74 and includes a planoconcave lens receiving a doubleconvex lens. As indicated, one side of the double convex lens is formedon a greater radius than the side abutting the plano-concave lens. As iswell known, chromatic aberration exists in lenses resulting from thedifferences of the index of refraction at different wave lengths. By thecompensating lens 74 formed of glasses having different refractiveindices, the focal point of the upper and lower wave lengths are broughtinto coincidence and the intermediate wave length (green) also coincidesfairly accurately. In this manner fall-off or loss of light at thecorners of the photograph can be maintained uniform for all sizes. Aspointed out previously, the light level around the margin of thephotograph is substantially equal to that in the center. In printingpictures in the popular sizes, the color compensating lens is not neededand may be omitted..

In FIG. 6, the solid line represents a theoretical curve of the threeadditive colors as measured by a spectral photometer, which arearbitrarily assigned a value of percent. The dash lines represent oneworkable solution to separating the wave lengths by the lens, filter anddiffusing system described above. The losses in intensity result fromseveral factors common to optical systems. These include intersurfacereiiections, scattering, absorption of light and the performance of therefiecting filters being somewhat less than one hundred per cent orperfect. This loss however is not critical so long as the actual curvesare maintained within the given wave lengths, as the level of intensityfor each lamp can be individually adjusted.

In operation, when initially set up for printing, an approximation ofthe color balance to be set on each of the various primary colors mustbe made. Several prints of a given negative are run in sequence withvisually selected for the printing paper used. Printing may nowcommence.

When changing from the first negative to subsequent negatives the lightmeasuring probe may be placed on the easel and the resistance adjustedto return the meter on the amplifier to Zero for each of the respectivecolors. Adjustment of one color does not affect the others. In thismanner an appropriate color balance for each negative may be rapidly andreadily obtained with a single test.

When the supply of paper has been exhausted, and a new supply is opened,the corrective factors given with the new supply may be noted.Compensation for changes in corrective factors relative to the previousbox may be readily obtained by appropriate resistance adjustment to addor subtract the numerical color corrective color compensating factor onthe meter scale. Printing may resume without the cut and try method toestablish a proper color balance. it can be appreciated that colorcorrective fac* tors will be now more meaningful in the present systemsince once the desired balance between colors is obtained, correctivefactors of new paper supplies may be compensated for through a simpleadjustment.

Of considerable importance in the measurement of the intensity of therespective colors in the selection of a wave length which is optimum forexciting the paper, and also within what is known to be the mostsensitive range for the measuring phototube. This is a phenomena bestillustrated by an example. In the infrared region above7G01'millimicrons, known types of phototubes are relatively insensitivewhile the paper is quite sensitive and responsive. Accordingly, the peakof the wave length in red region is controlled by filter selection tofall between the peak response of the known types of'paper which isquite broad, and the responsive wave Ilength of known type ofphototubes. The same applies to the selection of peak wave lengths forthe other colors in the color source. Accordingly, the wave length ofeach color at its peak will fall between the peak response of the tubeand paper. Accordingly, measurement of the intensity of each color priorto printing can be achieved to predetermine with great accuracy theintensity of the exciting light providing advantages formerly notavailable.

When portrait work is to be done, a second diffuser is inserted abovethe negative as at '73 in the space provided. This diffuser is a clearplastic having embossments which diffuse a small portion of thecollimated light to illuminate the side walls of negative scratches.When used in combination with the system above described and placedimmediately above the negative in a conventional type of condenserenlarger, it provides a soft portrait type diffusion to the print,obliterating minor skin blemishes and the like without interfering withthe trueness of the fiesh tones, eye color, hair color and otherfeatures.

After a consideration of the foregoing description of the invention, itbecomes apparent that the objectives set out above are readily achieved.It will become obvious to those skilled in the art that modificationsmay be made without departing from the inventive concepts embodiedherein. Therefore, only such limitations should be imposed as lareindicated by the spirit and scope of the appended claims.

We claim:

1. A color head adapted for use in condenser type enlargers, said colorhead comprising three light sources disposed at different elevations,multi film filter means to separate light emitted from each of saidlight sources into light rays having wave lengths falling within a bandidentifying separate color components, said multi film filter meansincluding means to blend said separated color components into a coaxialwhite light ray of transversely uniform intensity, and lens meansadapted to receive said coaxial white light and focus the same at afocal po-int coincidental with the focal point of a negative lens meansfor uniform transmission to a condenser system of an enlarger.

2. The color head of claim ll wherein diffusing means is disposedbetween said negative lens means and said condenser system of saidenlarger, said diffusing means including a semispherical type diffuser.

3. A color head adapted for use in condenser type enlargers, said colorhead comprising three light sources disposed at different elevations,multi film filter means to separate light emitted from each of saidlight sources into light rays having wave lengths falling within a bandidentifying separate color components, said multi film filter meansincluding means to blend said separated color components into a coaxialrefined white light ray of transversely uniform intensity, lens meansadapted to receive said ycoaxial refined white light and focus the sameat a focal point coincidental with the focal point of a negative lensmeans, first diffusing means adjacent said negative lens means todiffuse said coaxial refined white light, and second diffusing meansadapted to diffuse said coaxial refined white light for uniformtransmission to a condenser system.

4. A color head adapted to provide refined coaxial light for use inphotographic enlargers, said color head comprising a plurality of lightsources, means to collimate light from each of said sources into a beamof transversely uniform intensity, a first filter means disposed in thepath of each of said collimated light rays to separate light from eachof said light sources into one component of three primary colors of red,blue and green, second filter means disposed at an angle to each of saidfirst filter means to reflect and trim light from said each of saidfirst filter means into a more sharply defined component of the primarycolors while-simultaneously mixing said components into a beam ofcoaxial light rays of uniform intensity, and means to diffuse said lightrays for uniform transmission to a condenser system.

S. The system of claim i wherein a negative holder is provided belowsaid condenser system `and a diffuser is mounted above said negativeholder for use in printing portraits.

`6. A color head particularly adapted for use in condenser typeenlargers, `said color head comprising three separate light `sourcesdisposed at different elevations, collimating Imeans adjacent each ofsaid light sources, multi film filter means to separate collimated lightfrom each of said light sources into a single refined light ray, each ofsaid light rays having a -wave length defining one of three colorcomponents consisting of blue, green and red, said multi film filtermeans including means to blend said refined color components into acoaxial and further refined `white light ray of transversely uniformintensity, second lter means in the path of said coaxial white light toreject wave lengths above and below visible wave lengths, lens means tofocus Vsaid coaxial refined white light at a focal point -coincidentalwith the focal point of a negative lens means, first diffusing meansadjacent sai-d negative lens means to diffuse said white light, andsecond diffusing means adapted to spread said light for uniformtransmission to a condenser system.

7. The color head of claim 6 wherein said light sources are arranged sothat the light source of the green color component is disposed above thelight source of the red color component and the light source of saidblue color comopnent is disposed above both of the previously `mentionedlight sources whereby said means to blend said refined color componentsinto a coaxial refined light ray will further trim each of said colorcomponents.

8. A color control head adapted for application to a condenser-type ofenlarger, said color control head comprising three light source meansarranged in vertically spaced planes, individual intensity control meansfor each of said light source means, first and second lenses posltionedclosely adjacent said each of said light source means to collimate lightinto parallel rays, the first of said lenses being a positive meniscuslens and the second of said lenses being a double convex lens having thefocal point thereof coincidental with the focal plane of said firstlens, first multi filter means disposed perpendicular to the path ofeach of said collimated'rays to filter said light into collimated rayshaving a relatively narrow and identifiable band width, each of saidlight rays from each of said light source after passing said first ltermeans having a wave length which differs from the other light sourcemeans to provide light of the primary color components, second multifilter means disposed at an angle to each of said collimated andfiltered light rays from each of said light sources, each of said secondmulti filter means being angularly disposed relative to said collimatedand filtered light ray-s whereby each of said light rays will berefiected ofi:` of said second multi filter means to form a single lightray of uniform transverse intensity, aspheric lens means disposed in thepath of said white light ray to direct said `white light ray to thefocal point of a plano-concave lens, a diffusing type means adjacentsaid plano-concave lens to diffuse said white light ray passing throughsaid plano-concave lens and semispheric means to receive light passingthrough said diffusing means to further diffuse said light for passageinto a condenser system.

9. A color control head adapted for appli-cation to a condenser type ofenlarger in lieu of an existing light head, said color control headcomprising three light source means arranged one above the other, eachof said light source means having first and second lenses disposedadjacent said light source means to collimate light emitted from saidlight source means into perfectly parallel rays and direct the same toan axis disposed at an angle to said rays, multi filter means disposedin the path of said collimated light to reject all light falling outsidea given :band width, whereby three collimated light rays of diverse bandwidths will be disposed in substantially par-allelism in differentelevations, second multi filter means disposed at an angle to each ofsaid collimated and filtered light rays, each of said second multifilter means being angularly disposed relative to said axis and to thecollimated and filtered light ray whereby a portion will be reflectedoff of said second multi filter means, said portion of said light rayreflected off of each `of said multi filter means being directedparallel to said axis in a single coaxial white light ray of uniformintensity, asphericlens means disposed in the path of said white lightray and being adapted to direct the same to a negative lens systemhaving its focal point disposed .at the focal point of said asphericlens, first diffusing means disposed on one side of said negative lensland a second diffusing means to receive light from said diffusing meansand spread it for uniform transmission to a condenser system.

10. A color source adapted to provide refined light composed of threeprimary additive colors to an enlarger, said color source includingfirst, second and third light sources arranged in parallel planes, eachof said light sources including a lamp adapted to emit light of variableintensity, a collimating system adapted to collimate said light emittedfrom said lamp into anbeam of parallel light rays, first filter meansdisposed '1n the path of said light rays to reject a portion of saidcollimated light of an unwanted wave length, second filter meansdisposed atan angle to said collimated light passed by said first filtermeans, said second filter means passing all light of an unwanted wavelength while reflecting light of desired wave length, said second filtermeans of said first, second and third light sources being arranged incoaxial parallelism, said second filter means of said second lightsource being further characterized by passing a preponderance of lightrefiected from said second filter means of said first light source, saidsecond filter means of said third llight source being furthercharacterized by passing a preponderance of light reflected from thesecond filter means of said first and second light sources thereby toprovide a coaxial refined collimated beam of light, third filter meansto further refine said light primarily in the wave lengths outside thevisible region, and means to collect and diffuse said refined light fortransmission to an enlarger.

11. The color source of claim 1th wherein said means to collect anddiffuse said light Iincl-udes an yaspheric lens, and a-colorcompensating lens is disposed between said aspheric lens and said thirdfilter means to provide uniformity in light intensity when printingenlargements of substantial size.

12. The color source of claim 10 wherein said collirnating system ofeach of said sources comprises a positive meniscus lens and a doubleconvex lens, said positive meniscus lens being disposed adjacent saidlamp, said lenses being adapted to arrange light rays emitted from saidlamp into a parallel beam at right angles to said first filter means.

13. A color source adapted to provide refined light composed of additivecolor components of red, blue, and green, said color source includingthree light sources disposed at different elevations, each of said lightsources including a lamp having a filament with a finite dimension,collimating means to collect unrefined light emitted from said filamentand arrange it in parallel rays of transverse uniformity, a first filtermeans associated with each of said light sources and adapted to reject aportion of said unrefined light while transmitting the remaining portionof said light, a second filter means associated with each of said lightsources, said second filter means being disposed in the path ofcollimated light transmitted by said first filter means, said secondfilter means associated with each source being arranged in coaxialrelation whereby light rejected by each of said second filter means will`be arranged in blended coaxial relation with light rejected 'by each ofthe remaining filter means, third filter means disposed in the path ofsaid blended coaxial light to further refine the same, and lens means tocollect said light and diffuse the same into a semispherical diffusingmeans for transmission to a condenser system.

14. A color source adapted to provide light having `[blended componentseach of which is rened to a nonoverlapping wave length, said colorsource comprising three light sources disposed at different elevations,each of said light sou-rees emitting unrefined light from a filament offinite dimension, a collimating system to collect said light and arrangeit in a parallel beam of substantially transverse uniformity, a firstmulti filter means adjacent each of said collimatingsystems, said rstmultifilm filter means refining .light from each of said sources intoadditive primary colors of refined light having wave lengthscorresponding to that of red, blue and green, a lsecond multi filmfilter means associated with each of said light sources and refiectingthe primary colors of light, said second multi film filter means of saidred source passing blue and green light from two of said sources, saidsecond multi film filter means of said green source passing blue lightfrom one of said sources, third filter means adapted to reectultraviolet wave lengths while suppressing infrared wave lengths therebyproviding a collimated beam of light -composed of three additive primarycolors of readily identifiable and non-overlapping Wave lengths,aspheric lens means adapted to receive said refined light yand direct itto a negative lens means, and semisphere means receiving said light fortransmission to an enlarger system.

15. The color source of claim 14 wherein said rst, second and thirdiilter means provide 'blended red, blue and green light, each of whi-chhas a peak response intermediate that 4of known types of paper to beprinted and known types of measuring phototubes.

16. A color head adapted for use in condenser type i enlargers, saidcolor head comprising three light sour-ces disposed at differentelevations, multilm filter means to separate light emitted from each ofsaid light sources into light rays having Wave lengths falling Within ahand identifying separate color components, said multi lm filter meansincluding means to blend said separated color components into a coaxialwhite light ray of transversely uniform intensity, said multi filtermeans selecting wave lengths in each of sa-id bands of said separatecolors which lfall Ibetween the known peak response of the paper to be.printed and that of known types of phototubes, and lens means adaptedto receive said coaxial white light and focus the same at a focal pointcoincidental with `the focal point of a negative lens means for uniformtransmission to a condenser system of an enlarger.

References Cited UNITED STATES PATENTS 12/1965 Remesat 88-24 l/l966Dauser 88-24

1. A COLOR HEAD ADAPTED FOR USE IN CONDENSER TYPE ENLARGERS, SAID COLORHEAD COMPRISING THREE LIGHT SOURCES DISPOSED AT DIFFERENT ELEVATIONS,MULTI FILM FILTER MEANS TO SEPARATE LIGHT EMITTED FROM EACH OF SAIDLIGHT SOURCES INTO LIGHT RAYS HAVIN GWAVE LENGTHS FALLING WITHIN A BANDIDENTIFYING SEPARATE COLOR COMPONENTS, SAID MULTI FILM FILTER MEANSINCLUDING MEANS TO BLEND SAID SEPARATED COLOR COMPONENTS INTO A COAXIALWHITE LIGHT RAY OF TRANSVERSELY UNIFORM INTENSITY, AND LENS MEANSADAPTED TO RECEIVE SAID COAXIAL WHITE LIGHT AND FOCUS THE SAME AT AFOCAL POINT COINCIDENTAL WITH THE FOCAL POINT OF A NEGATIVE LENS MEANSFOR UNIFORM TRANSMISSION TO A CONDENSER SYSTEM OF AN ENLARGER.